The invention relates to a control apparatus for regulating the addition of supplementary fresh air to the exhaust gas of an internal combustion engine. The engine is of the type which includes an exhaust gas post-combustion system located in the exhaust system and an oxygen sensor, also located in the exhaust system, for monitoring the composition of the exhaust gas.
It is known to provide detoxication systems for internal combustion engines, which include thermal and/or catalytic reactors for transforming toxic exhaust constituents, such as carbon monoxide (CO), hydrocarbons (C.sub.x H.sub.y) and oxides of nitrogen (NO.sub.x) into harmless chemical compounds. Since an internal combustion engine is normally operated with variable load factors, the composition of the exhaust gases is subject to changes. These changes disturb the post-treatment of the exhaust gas in the thermal and/or catalytic reactors, with the result that the oxygen content of the exhaust gas is sometimes too high and sometimes too low. In order to avoid this disadvantage, it is known to operate the internal combustion engine with a shortage of air (.lambda. &gt; 1.0) and to supply the air required for combustion in the post-treatment system by means of an air pump driven by a motor. An arrangement of that type is described and illustrated in German laid-open specification No. 2,035,591.
It is also known to regulate the admission of supplementary air to the exhaust gas in dependence on the induction tube pressure and on the rpm of the internal combustion engine. In such a known regulator, an auxiliary control loop superimposes a precise adjustment of the supplementary air quantity in dependence on the composition of the exhaust gas. An arrangement of that type is described and illustrated in German allowed application No. 2,254,961.